"It is very important musically, historically and humanly," he says. "The score was smuggled out of the camp on separate bits of paper. It was a scholarly work to piece it together, it was so fragmentary."
The camp in question was the Austrian-built garrison town of Terezin in Bohemia-Moravia (part of future Czechoslovakia), which the Nazis transformed in 1941 into a ghetto and then into a unique concentration-cum-transit camp. Under its Germanised name of Theresienstadt, it fed the extermination camps in Poland from 1942 until Germany's defeat in 1945.
But until the Jewish inmates were transported, they were allowed and, indeed, encouraged to create and enjoy an extraordinary musical and artistic life amid acute deprivation, overcrowding and disease.
The population included the established composer, Viktor Ullmann, who produced an impressive body of music there, with songs, sonatas and stage works.
Although Ullmann had studied under Schoenberg and paid tribute to him in his 1925 Schoenberg Variations, his style changed completely when he came into contact with the Yiddish and Zionist songs of eastern Jewry in Terezin. A distinctive new voice was forged, delicate and yearning. No atonality here.
So why, of all things, has Conway chosen to preface Ullman's parable with a Bach Easter cantata? (The opera's surrealistic plot centres on Death's revolt against the industrialisation of death with its ever-increasing workload and loss of dignity. Death only agrees to end his strike and release people from eternal life when the Emperor agrees to be the first to die.)
Yes, Bach was a major influence on Ullmann, who makes several musical references to him. But this particular cantata has the title Christ lag in Todesbanden (Christ Lay in Death's Bonds), with words by the deeply anti-semitic Protestant reformer, Martin Luther. Hardly endearing to a Jewish audience.
For Conway it is purely a stageing issue, like his decision to restrict the small chamber orchestra to the instruments available to Ullmann, including banjo and guitar.
"The opera is too short to stage on its own. But pairing it with something else would be to diminish it. It needs to stand alone. This way the performance is lengthened but remains musically related," he says.
It took a Jewish musician to explain to Conway the sensitivities involved. Jonathan Gale is a vocal coach, conductor and repetiteur (rehearsal pianist) who followed his music degree at Cambridge with studies at St Petersburg Conservatoire, the Guildhall School of Music and Drama, and National Opera Studio.
Gale knows the Ullmann opera well from a Guildhall student production, where he was repetiteur at rehearsals and orchestral harmonium player in performance. He is also married to the soprano in this production, Tennessee-born Paula Sides.
After studying at the Schwob School of Music in Georgia, Sides came to the Royal College of Music in London. She met her husband when he sat in the audience at a student concert and she sang on stage. They married at St John's Wood Liberal Jewish Synagogue three years ago.
Gale is another Ullmann fan."He has been unjustly neglected," he says. "Recognition is long overdue."
After researching Ullmann's work, especially the Terezin-composed manuscripts, Gale accompanied his wife in an Ullmann song recital earlier this year for ETO sponsors. The concert was held at the home of Lady Solti, widow of the former Royal Opera House conductor (and Hungarian-Jewish wartime refugee), Sir Georg Solti.
The success of the concert has led to a further lecture-recital date for the couple. "The music is so accessible," says Sides. "It is a bridge between romanticism and modernism."
Aware now of the Bach problem (the words not the music), Conway is at pains to stress that he sees the composition as an expression of hope, the triumph of life over death. Plus the fact that it is sung in German, melding into the actual opera, which is sung in English.
Conway notes the tension between Ullmann's gentle, haunting music and the harsh, bitter lines written by his young librettist, Peter Kien. Ullmann was 44 when he was sent to Terezin and had made his name. Kien was just reaching 23. A prodigious talent, he felt keenly the snatching away of life and opportunity.
Apart from Kien's literary output, his hundreds of drawings disproved the Nazi "model camp" propaganda which fooled the Red Cross delegation on its notorious visit in June 1944. According to Conway: "You can feel the pain in his writing."
Interestingly, although Ullmann identified with his Jewish fellow-prisoners, he was baptised at birth as a Catholic. His Jewish parents converted so that his father could fulfil his ambition of becoming an officer in the Austrian imperial army.
Viktor, however, was never militaristic and, like other assimilated Jewish intellectuals of his era, had spiritual and philosophical leanings.
Given these Jewish roots, and Conway's undisguised enthusiasm for this "beautiful opera", it seems crazy that its two London dates -- plus Exeter -- of the six-week run from October to mid-November (it tours with Benjamin Britten's Albert Herring and Peter Maxwell Davies' The Lighthouse) are on Friday nights.
There is no problem with the dates for Cambridge, Tunbridge Wells, Harrogate, Aldeburgh, Malvern Priory and Buxton.
To make up for that, a semi-staged performance will be given at the North Western Reform Synagogue, Alyth Gardens, but without the Bach cantata. "It would not be right for shul," affirms Paula Sides.
Programmes start with a pre-performance talk on the opera's history and background, with added interest from local children performing songs inspired by poems written by Terezin children. The interval follows, then the opera. Ticket-holders can skip the talk but Conway finds that audiences appreciate the input.
And what happened to the original production? The familiar, tragic story. Musicians, singers and stagehands were, like the rest of the inmates, deported to Auschwitz.
It is not certain whether it was Nazi suspicions of a resemblance between the Emperor character and Hitler that led to the dress rehearsal being the last performance. But there was no first night as planned in autumn 1944.
Instead, in October 1944, Ullmann, Kien and all remaining production members were sent to their death in Auschwitz.
